Your Good Health: Diet, exercise beat BMI on road to a longer life

Dear Dr. Roach: I am an 81-year-old man in good health. I am 5 feet, 11 inches tall and now weigh 175 pounds after intentionally losing 15 pounds through a combination of diet and exercise. I feel better at this weight than I did at my former weight, but my doctor says the studies he has read show that if a person is slightly overweight, he is likely to live longer than a person who weighs less. Do you agree with his position?

D.N.K.

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This is an area of research that has created a great deal of controversy. We have long known that being very thin is associated with a high mortality, and being morbidly obese also is associated with a high risk. The optimum level of BMI (body mass index, an imperfect way of expressing weight adjusted for height) for longevity has changed over time. Previous studies postulated a very thin BMI of 22, as the one associated with lowest risk of death. However, your doctor is right that most of the newer research has identified that what was formerly considered slightly overweight, a BMI of 26 to 28, has a lower overall mortality risk than a lower BMI. In your example, your BMI went from 26.5 to 24.5.

However, the situation is far more complex and nuanced. A healthy diet probably has more impact on mortality than a small change in BMI. Exercise almost certainly has a more beneficial effect. Most important of all, the relationship between BMI and mortality does not imply causation; that is, it might not be that being too thin increases the risk of death. It is likely that much of the apparent risk of death from being too thin comes from the fact that many people who are very thin are that way because of illness. As I said, researchers have disagreed on the best way to evaluate this and other data analysis methods.

I think that what you told me about feeling better with your new weight is important, and that listening to your body is critical. I don’t recommend that people who are mildly overweight lose weight just to lose weight. There are unhealthy ways to lose weight, which probably do more harm than good. I would recommend a healthy diet with lots of fruits and vegetables, whole grains, nuts and fish, and modest amounts of red meat. I also strongly recommend a regular exercise regimen, which need be no more complicated than a daily walk, building up to at least an hour a day (but it doesn't have to be all at one time). Pay more attention to diet and exercise, and let the weight take care of itself.

Please note, though, that I am talking about those who are mildly overweight. Most people with more serious weight issues do benefit from weight loss, in terms of preventing or lessening the effect of weight-related conditions, such as Type 2 diabetes and osteoarthritis.

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